Phase regulator for multifrequency generators



July 28,- 1925.

PHASE REGULATOR FOR MULTIFREQUENCY GENERATORS Filed July 11, 1924Eewmads' A TTORNE Y Patented July 2 8, 1925.

UNIT-ED STATES v1,541,217 PATENT oFFIcs.

JOSEPH HERMAN, OF NEW YORK, N. Y., ASSIGNOR TO AMERICAN TELEPHONE ANDTELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

TEASE REGULATOR FOR MULTIFBEQUENCY GENERATORS.

Application filed July 11, 1924. Serial No. 725,504.

. for purposes of illustration, mi ht be foun in certain types ofcarrier te egraph systems which provide for multiplex telegraphy withdiscrimination by difference of phase between messages in the samefrequency range. At the receiving end of such systems reception is bythe homodyne method and a local enerator generates currents correspon into the various carrier channels utilized. it is essential in suchsystems that these local currents be in the proper phase relationshipwith the carrier currents transmitted from the sending station and foraccomplishing this purpose the arran 'ements of the invention areparticularl uselul and accordingly, the invention will e illustrated inconnection with a telegraph system of this type. Such a system isillustrated in a copending application, Serial No. 696,048, filedFebruary 29, 1924-, in the name of H. Nyquist, and reference is hadthereto for a more. detailed description thereof. It, is understood,however, that its application is not limited thereto but that 1t may beutilized in many other ways. A articular feature of the arrangements ofte invention consists in the provision of a multiplying device by meansof which difierences in phase between the two enerators may multiplied anumber of times. This magmfication of error is then utilized to givevery accurate and automatic adjustment of pne of the generators tosecure and maintain the desired phase relationship. Other features anddetails of the arrangements of the invention will appear more fully fromthe detailed description hereinafter given.

In the drawing is shown a circuit diagram embodying a preferred form ofthe invention. The drawing illustrates a multiplex telegraph line Lterminating at a receivin station. At the sending station, which isgenerated at the sending station.

tween messages on the same carrier fre quency. These carrier frequencieswill be transmitted over line L to the receiving eta-- tion, where theywill be transmitted over circuit 7 and thence the separate carrierfrequencies. will be selected by the filters 27 and 28 and transmittedover circuits 8 and .9 to the receiving apparatus R, and R The receptionat this ap aratus is accomplished by the well known homodyne methodandhence it is necessar to supply to the receiv ng arrangements 1%, andR frequencies similar to and with a pro er phase relationship to thecarrier re uencies or this purpose the circuits 10 and 11 and themultifrequency generator 3 are provided. In order to control andregulate the phase of the currents generated by the multi-freuencygenerator 3 a certain synchronizing requency, which may be termed F, issent out from the sendin station. This. synchronizing frequency istransmitted through the filter 1 and the amplifier 2 and then connectedto a synchronous motor M. The synchronous motor M is o erated by thiscurrent and is geared to t e shaft of the multi-frequency generator 3and serves as a speed re ulator to maintain it in approximate syncronism with the generator at the sending station. However, othermechanism than t e motor M might be used for this purpose, such forexample, as a centrifu al governor on the driving motor M. e maindriving power for the generator is obtained from a direct current motorM, which is geared to the shaft of the nerator. The motor M includesashunt eld 6, a field resistance 5, and an armature resistance 4 by meansof which the phase re ulator maintains the proper phase relations ipbetween the multi-fre uency generator 3 and the enerator at the istantstation.

e operation of re lation is as follows: Part of the synchronizingfrequency F is transmitted over circuit 12 to the transformer 13 andthence to the grid of a detector tube 14, which is designed to functionas an harmonic producer. The output of this detector contains a numberof harmonics of the input frequency F, and any one of these harmonicsmay be used for the phase regulation. It is desirable to use a fairlyhigh harmonic if very close phase regulation or synchronism is required.This 1s true because any change in phase of the fundamental frequencywill be multiplied by the harmonic ratio in the various harmomcfrequencies. It is evident, therefore, that the higher the harmonic thegreater will be the effect upon the phase regulator of a given phasechange in the fundamental. The various harmonics in the plate circuit ofthe harmonic producer 14 are connected through I a transformer to afilter 15. This filter is designed so that only the desired harmon c,which may be termed F passes through 1t. After passing through thefilter this harmonic F is made to pass through a variable hase shifterdevice 16, which is well known in the art, which permits of any desiredphase adjustment of this frequency. From the output of the phase shifter16 the fre quency F is connected diflerentially to a' duplex vacuum tubedetector 20 of the balanced type through the transformer 17 A frequencyF similar to the frequency F will be supplied from the multi-frequencygenerator 3 to the circuit 19 from when 1t will be applied in parallelaiding to the grids of the balanced detector 20 by the transformer 18.Connected to the output of I the balanced detector 20 is a polar relay21. By now adjusting the phase of the frequency F by means of the phaseshifter device 16 so that the frequency F will be 90 out of phase withthe frequency F the detector current through the two windings of thepolar relay 21 will be equal and have no effect upon the relay. Underthis condition the polar relay will vibrate unbiased under the influenceof reversals applied to circuit "25 and the third-windin of the relay.The

armature resistance 4 an the field resistance 5 of the directcurrentmotor M, which are connected as shown to the contacts of this relay,will therefore be short-circuited for one half of the time and the motorwill tend to run at a predetermined desired speed. Should either of thegenerators at the different stations tend to change their speed thephase relationshi between the frequencies F and F will 0 ange veryrapidly because of the multiplying effect of these high frequencies.This will destroy the condition of balance in the detector 20 andproduce unbalanced currents in the windings of polar relay 21 which willbias the vibrating armature of the relay to one contact or the other. Abias to the contact 23 tends to increase'the speed of the motor byshort-circuiting 'the armature resistance 4 for a longer-period .of timethan the field resistance 5 and a bias to contact 24 will tend todecrease the speed for the opposite reason.

It is evident that this tendency of the relay to change the speed of thelocal generator is so related to the causes which produced theunbalanced current that the phase relationship between F, and F willtendto be restored. By utilizing very high harmonics of thesynchronizing frequency F it is evident that a small change of phase canbe made to produce a very large restoring force.

While the invention has been disclosed as embodied in certain specificarrangements and illustrated in connection with telegraphic circuits, itis understood that it is capable of embodiment in many and widely variedforms without departing from the spirit of the invention as defined bythe appended claims.

What is claimed is:

1. A transmission line interconnecting two stations, generators at eachof said stations, means at one of said stations for applying to saidline from the generator thereat current of a certain frequency, means atthe other station for producing harmonics of said frequency, and meansat said last mentioned station controlled by variations in the phase ofone of said harmonics for controlling the generator thereat.

2. Arrangements for controlling the phase relations between generatorsat different stations comprising a generator at each of said stationsand a transmission line interconnecting said stations, means at one ofsaid stations for selecting one of the frequencies applied tosaid'linebythe generator at the other station, means for producing harmonies ofsaid frequency, means for selecting one of said harmonics, and meanscontrolled by variations in the phase of said harmonic for controllingthe generator at said station.

3. Arrangements for controlling the phase relations between generatorsat distant stations comprising generators at each of said stations, atransmission line interconnecting said stations, and arrangements at oneof said stations comprising means for selecting one of the frequenciesapplied to the line from the generator at the distant station, means forproducing harmonics of said frequency, means for selecting one of saidharmonics, a balanced detector, a polar relay in the output circuitthereof, means controlled by said polar relay for controlling 'thegenerator at said station, means for applying from said generator tosaid detector a beating current similar in frequency to said selectedharmonic, and means for adjusting the phase of said selected harmonic sothat it will be 90 out of phase with said beating current and for"applying said harmonic to said detector;

'4. Arrangements for controllin the phase relations between generatorsat distant stations comprising generators at each of said stations, atransmission line interconnecting said stations, and arrangements at oneof said stations comprising means for selecting one of the frequenciesapplied to the line from the generator at the distant station,

means for producing harmonics'of said frequency, means for selectingone, of said harmonies, a balanced detector, a vibrating polar I relayin the output circuit thereof and con- 10 trolled thereby, drivingmechanism for the generator at said statlon, control circuits for saiddriving mechanism controlled by said vibrating polar relay, means forapplying from said generator to said detector a beating current similarin frequency to said selected harmonic, and means for adjusting the haseof said selected harmonic so that it Wlll be 90 out of phase with saidbeating current and for applying said harmonic to said detector. I

In testimony whereof, I have signed my name to this specification this8th day of July 1924.

JOSEPH HERMAN.

